The present invention relates to heat exchangers and more particularly to one of the evaporative type having an improved, more efficient, air circulation and water distribution means.
U.S. Pat. No. 3,385,352 is typical of prior art heat exchangers or condensers in that it employs a fan having blades of identical pitch which are rapidly rotated to draw air from the outside down over and through the coils and up past the fan blades to exhaust. At the same time water is drawn from a sump by a centrifugal pump rotated with the fan blades and deposited into a trough above the coils from which it flows down over the coils by gravity. The efficiency of these prior art exchangers was relatively low due primarily to the large amount of electrical power required to rotate the fan blades sufficiently fast to insure necessary air flow over the coils for proper heat transfer. In addition, dripping of the water over the coils did not result in a sufficient amount of the surface area of the coils coming in contact with the water. For comparison, a typical evaporator of the prior art which requires a 40,000 cubic feet per minute air flow at a one-half inch static air pressure would need a fifteen horsepower motor to drive a plurality of fans at approximately 1750 rpm and approximately three additional horsepowers would be required to operate the water distribution pump. In contrast, as a result of Applicant's unique two-stage (pushing and pulling) fan blade design and sling-type water distribution system, significant power savings can be realized while achieving the same amount of cooling. Applicant's design requires only a one and one-half horsepower motor to rotate a single large, two stage fan at approximately 100 rpm to thereby achieve the same 40,000 cubic feet per minute rate of flow at a one-eight inch static air pressure and only one-fourth additional horsepower would be required to operate the water distribution pump due to its unique design. This reduced static pressure results from the fact that the water and air move in the same direction unlike prior art evaporators.
Applicant achieves this phenomenal efficiency by his unique two-stage fan blade design which requires a fraction of the horsepower needed by the prior art evaporators to circulate the same quantity of air through the cooling coils. Applicant's fan relies on the well known fact that on a typical fan blade, 80 percent of the work is done by the outer end 20 percent of the blade. Thus, by mounting the fan blades for rotation above both the air inlet to the coils, as well as the outlet from which the air is being exhausted and having the first stage or outer approximately 20 percent of the fan blades pitched to force air into the inlet and the second stage or inner approximately 80 percent of the fan blades pitched in a direction opposite to those of the first stage to draw this air out the exhaust outlet, a large quantity of air can be circulated over the coils by rotating these blades slowly in comparison to similar fans of the prior art devices. Applicant's unique blade design will be more fully explained later. In addition, Applicant's device can constantly distribute cooling water or other liquid heat transfer medium such as glycol brine or the like, over the coils as the fan blades rotate. This is achieved by a novel pump which relies on centrifugal force to withdraw water from a sump and in effect "sling" it over the coils as the pump rotates with the fan blades. Air forced by the fan blades of the first stage engages this cooling water and insures complete distribution over the coils while simultaneously reducing the static air pressure in front of the fan blades of the first stage as aforementioned.
It is therefore the primary object of the present invention to provide an improved and highly efficient heat exchanger.
It is another object of the present invention to provide a device of the subject type which utilizes a novel two-stage (push and pull), slow moving, fan blade arrangement having two sets of blades to achieve air flow through the device.
It is a further object of the present invention to provide a device of the subject type that has incorporated in it a more efficient pump that acts to "sling" the water over the coils as the fan blades rotate in the same direction as the pump.
It is yet another object of the present invention to provide a device of the subject type that, due to its simple construction and use of materials that do not easily corrode or deteriorate from exposure to the elements, is relatively less expensive to operate and maintain than similar prior art devices.